1. Field of the Invention
This invention relates to an improved process for homogeneously hydrogenating polycyclic aromatic hydrocarbons thereby producing partially hydrogenated derivatives thereof, under mild conditions utilizing anionic Group VIII metal hydride compositions as catalysts.
2. Brief Description of the Background of the Invention Including Prior Art
Partially hydrogenated polycyclic aromatic hydrocarbons are known in the art as being useful organic solvents and intermediates. Particularly known are the tetrahydro derivatives, such as 1,2,3,4-tetrahydronaphthalene, also known as "tetralin."
Various processes are known in the prior art whereby fully saturated products are obtained from the homogeneous catalytic hydrogenation of aromatic and polycyclic aromatic hydrocarbons. See J. Amer. Chem. Soc., Vol. 96, p. 4063 (1974); ibid., Vol. 97, p. 237 (1975); ibid., Vol. 97, p. 1266; ibid., Vol. 99, p. 7395 (1977); and Inorganic Chemistry, Vol. 15, p. 2379 (1976).
Relatively few processes are described for selectively producing partially hydrogenated products of polycyclic aromatic hydrocarbons under homogeneous catalytic conditions.
The reference, J. Org. Chem. 24, p. 1287 (1959) describes the homogeneous partial hydrogenation of polycyclic aromatics using dicobalt octacarbonyl. However, the process requires temperatures from 135.degree.-200.degree. C., pressures in the range of 2800-3600 psig and an atmosphere of synthesis gas, being a mixture of 1:1 molar ratio of H.sub.2 /CO.
The reference J. Org. Chem. 37, p. 3915 (1972) describes the homogeneous partial hydrogenation of anthracene producing 9,10-dihydroanthracene using cobalt hydrocarbonyl. However, the reaction requires an atmosphere of CO and H.sub.2, and is not described as producing the 1,2,3,4-tetrahydro derivative of anthracene.
The reference, J.C.S. Chem. Comm., p. 427 (1977) describes the homogeneous partial hydrogenation of anthracene using di-M-chlorodichlorobis(pentamethylcyclopentadienylrhodium) (I) as the catalyst. However, in the process 15 equivalents of base, (such as triethylamine) per mole of catalyst, were used and gave a mixture of tetrahydro- and octahydroanthracenes.
The reference, Indian J. Chem., Vol. 14A, p. 107 (1976) describes the use of a mixture bis(acetylacetonato) cobalt (II) and nickel (II) hydrates, treated with LiAlH.sub.4 reducing agent, as capable of reducing naphthalene to tetralin and decalin. However, the process requires the in situ preparation of the catalyst, a temperature of about 150.degree.-200.degree. C., and reaction pressure of hydrogen of about 40-120 kg/cm.sup.2 gauge (about 36-108 atmospheres).
What is desired and what the prior art does not describe are catalysts which are effective in partially hydrogenating polycyclic aromatic hydrocarbons particularly producing tetrahydro derivatives thereof, under homogeneous and mild conditions of temperature and pressure in which the presence of a basic reagent or carbon monoxide atmosphere, are not required.